1. Field of the Invention
The present invention relates to a charging apparatus of a bicycle dynamo. In particular, the present invention relates to a charging apparatus that is charged by a voltage generated by a bicycle dynamo to allow efficient and stable charging when a dynamo output changes without a steady travel speed.
2. Background Information
In recent years, some bicycles are equipped with an automatic transmission. An electrically-driven transmission has been used as the automatic transmission of the bicycles. These types of bicycle are usually equipped with a dynamo for driving the electrically-driven transmission as well as a charging system for charging a storage device from a voltage generated by the dynamo. Because the voltage generated by the dynamo is an alternating current voltage, half-wave rectification or full-wave rectification is performed in the charging system.
However, a voltage generated from the dynamo for bicycle fluctuates, i.e., increases or decreases, depending on the travel speed of the bicycle. For example, when the bicycle is traveling at a low speed, a voltage generated by the dynamo is small. In such a case, there is a chance that a sufficient voltage cannot be supplied to electrical components of the bicycle, such as an electrically driven transmission, and thus, there is a risk that these components will malfunction.
In view of the above, Japanese Laid-Open Patent Publication No. 2002-262473 discloses a voltage-doubling rectifier circuit used to charge an electric power from a dynamo and supply stable electrical power to electrical components of a bicycle.
Moreover, a charging apparatus of a bicycle dynamo is preferably configured and arranged to obtain stable electrical power using a simple circuit. FIG. 5 shows one example of the simple circuit configuration of a conventional half-wave voltage-doubler circuit. More specifically, a charging circuit with the half-wave voltage-doubler circuit shown in FIG. 5 basically comprises a capacitor C1 used as a charging element, a pair of diodes D1 and D2 connected between a dynamo GE for a bicycle and the capacitor C1, and a capacitor C2 connected between a connection point of the diodes D1 and D2 and a second terminal of the dynamo GE.
In the circuit shown in FIG. 5, the capacitor C2 is charged by the output of the dynamo GE through the diode D2 during the negative (−) half-cycle of the output of the dynamo GE. During the inverse half-cycle, the electrical charge stored in the capacitor C2 is supplied to the capacitor C1 through the diode D1 to charge the capacitor C1. This configuration makes it possible to obtain an output voltage V1 of the capacitor C1 that is higher than the peak voltage of the dynamo GE.
However, since the output frequency in the dynamo GE changes depending on the speed at which the bicycle is traveling, it is difficult to determine an optimum capacity for the capacitor C2. Depending on the capacity of the capacitor C2, an electrical charge at the opposite polarity will be stored in the capacitor C2 during the inverse half-cycle while the capacitor C2 is discharging. In such a case, charging the capacitor C2 during the next half-cycle will require more time, and thus, charging the capacitor C2 cannot be performed efficiently.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved charging apparatus for a dynamo for a bicycle. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.